Port fuel direct injection (PFDI) engines include both port injection and direct injection of fuel and may advantageously utilize each injection mode. For example, at higher engine loads, fuel may be injected into the engine using direct fuel injection for improved engine performance (e.g., by increasing available torque and fuel economy). At lower engine loads and during engine starting, fuel may be injected into the engine using port fuel injection to provide improved fuel vaporization for enhanced mixing and to reduce engine emissions. Further, port fuel injection may provide an improvement in fuel economy over direct injection at lower engine loads. Further still, noise, vibration, and harshness (NVH) may be reduced when operating with port injection of fuel. In addition, both port injectors and direct injectors may be operated together under some conditions to leverage advantages of both types of fuel delivery or in some instances, differing fuels.
In PFDI engines, a lift pump (also termed, low pressure pump) supplies fuel from a fuel tank to both port fuel injectors and a direct injection fuel pump (also termed, a high pressure pump). The direct injection fuel pump may supply fuel at a higher pressure to direct injectors. During operation, one or more hot spots may be formed on a bottom surface of a pump piston within the direct injection fuel pump. As such, fuel may be exposed to the bottom surface of the pump piston when residing within or flowing through a chamber (herein termed a step room) formed underneath the bottom surface of the pump piston. Accordingly, fuel may be heated leading to fuel vaporization within the step room. Further, the evaporation of fuel may overheat the step room and may increase a likelihood of the pump piston seizing within a bore of the direct injection fuel pump.
An example approach shown by Marriott et al. in US 2013/0118449 enables cooling of the step chamber via fuel circulation. Herein, fuel from a low pressure fuel supply line is circulated to the step room of the direct injection fuel pump and thereupon returned to the low pressure fuel supply line upstream of an accumulator. Further, the flow of fuel through the step room is primarily driven by a change in volume of the step room due to pump piston motion.
The inventors herein have recognized a potential issue with the example approach of Marriott et al. For example, a direct injection fuel pump may include a pump piston coupled to a piston stem of substantially the same exterior diameter as the pump piston. By using a piston stem with a similar exterior diameter as the pump piston, pump reflux from the step room may be reduced. In this case, the volume of the step room may not vary significantly during pump strokes. Further, without a significant change in the volume of the step room, fuel circulation through the step room may be reduced, and step room cooling may not occur.
The inventors herein have recognized the above issue and identified an approach to at least partly address the above issue. In one example approach, a method may comprise, when a spill valve is in a pass-through state, circulating a portion of fuel from a compression chamber of a direct injection pump to a step room of the direct injection pump, the circulating including flowing the portion of fuel through the spill valve and drawing the portion of fuel into the step room from upstream of the spill valve and downstream of an accumulator. In this way, the step room may be cooled by reflux fuel from the compression chamber.
In another example approach, a system may comprise an engine, a lift pump, a direct injection fuel pump including a piston coupled to a piston stem, a compression chamber, a step room, and a cam for driving the piston, a high pressure fuel rail fluidically coupled to an outlet of the direct injection fuel pump, a solenoid activated check valve positioned at an inlet of the direct injection fuel pump, a fuel supply line fluidically coupling the lift pump and the solenoid activated check valve, an accumulator positioned upstream of the solenoid activated check valve, the accumulator fluidically communicating with the fuel supply line, a first check valve coupled to the fuel supply line between the accumulator and the solenoid activated check valve, a first fuel conduit including a second check valve, a first end of the first fuel conduit fluidically coupled to the fuel supply line between the first check valve and the solenoid activated check valve, a second end of the first fuel conduit fluidically coupled to an inlet of the step room, a second fuel conduit, a first end of the second fuel conduit fluidically coupled to an outlet of the step room, and a second end of the second fuel conduit fluidically coupled to the fuel supply line at the accumulator upstream of the first check valve and downstream of a third check valve. This example system may enable isothermal fuel flow through the direct injection fuel pump.
For example, a direct injection (DI) fuel pump of a fuel system in a PFDI or a DI engine may include a compression chamber, a pump piston coupled to a piston stem, and a step room. In one example, the piston stem may have an external diameter that is substantially equal to an external diameter of the pump piston. The DI fuel pump may receive fuel into its compression chamber via a fuel supply line from a lift pump. An electronically controlled solenoid activated check valve, fluidically coupled to the fuel supply line, may be arranged at an inlet of the compression chamber of the DI fuel pump. An accumulator may be positioned upstream of the solenoid activated check valve to store fuel during a compression stroke in the DI fuel pump. A first check valve located between the accumulator and the solenoid activated check valve may obstruct fuel flow from the solenoid activated check valve to the accumulator while allowing fuel flow from the accumulator towards the solenoid activated check valve. Further, the step room may fluidically communicate with the fuel supply line via each of a first fuel conduit and a second fuel conduit. The first fuel conduit may fluidically couple an inlet of the step room to the fuel supply line between the first check valve and the solenoid activated check valve. The second fuel conduit may enable fluidic communication between an outlet of the step room and the fuel supply line at the accumulator. Further, a third check valve may be coupled to the fuel supply line downstream of the lift pump and upstream of a node where the second fuel conduit merges with the fuel supply line at the accumulator. Thus, when the solenoid activated check valve is de-energized to a pass-through state, a quantity of fuel (e.g., reflux fuel) may exit the compression chamber of the DI fuel pump through the solenoid activated check valve. As such, the quantity of fuel may exit the compression chamber during a compression stroke in the direct injection fuel pump. Since the first check valve impedes fuel flow towards the accumulator, the quantity of fuel may initially flow to the step room via the first fuel conduit. The quantity of fuel may then flow from the step room towards the accumulator via the second fuel conduit. Thus, the circulatory flow of the quantity of fuel may cool the step room.
In this way, fuel heating within the step room of the DI fuel pump may be reduced. By flowing fuel from the compression chamber to the step room, pump strokes within the compression chamber (and not within the step room) may drive fuel flow through the step room. Thus, fuel within the DI fuel pump may be maintained substantially isothermal. By reducing fuel heating in the step room, fuel vaporization within the step room may be diminished leading to enhanced DI fuel pump performance. Overall, durability of the DI fuel pump may be extended, and maintenance costs may be decreased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.